• S C Agarwal

      Articles written in Pramana – Journal of Physics

    • Bond constraint theory and the quest for the glass computer

      S C Agarwal M A Paesler D A Baker P C Taylor G Lucovsky A Edwards

      More Details Abstract Fulltext PDF

      Electronic switching in amorphous chalcogenide semiconductors has been observed and studied for nearly forty years. Technological exploitation of this phenomenon has most recently emerged in DVD's where GST, a compound of germanium, antimony, and tellurium, is used to store information. We explain how GST behaves as a switch and how X-ray absorption fine structure can be used to unlock the specifics of the switching process. The tool that leads to this deeper understanding is the bond constraint theory. We explain how this theory leads to an explanation of switching and of the behavior and properties of amorphous materials in general. Finally, the prospects for developing GST-related materials into non-volatile memory media that could be the basis for glass computers are discussed.

    • Durability of rewritable phase-change Ge$_{X}$Sb$_{Y}$ Te$_{1−X−Y}$ memory devices

      N Parvathala Reddy Ch Bapanayya Rajeev Gupta S C Agarwal

      More Details Abstract Fulltext PDF

      The bond constraint theory (BCT) dealing with the rigidity caused by bond constraints and the long-range potential fluctuations (LRPF) arising from the defects and heterogeneities in the disordered semiconductors are important for understanding the atomic and electronic properties of amorphous semiconductors. Here, they are applied to the already commercialized Ge$_{X}$Sb$_{Y}$ Te$_{1−X−Y}$ (GST) chalcogenide glasses used in the rewritable phase change memory (PCM) devices. The main concern at present is to improve their ability to withstand a large number of phase change cycles, by choosing the right composition. The two considerations (BCT and LRPF) are briefly described and tested on the most commonly used Ge2Sb2Te5 and the nearby compositions. While these considerations provide significant insight into their atomic and electronic structures, the ansatz linking them with the durability of the PCM devices need to be justified by more work.

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